Abstract:

Use of montmorillonite as sorbents to remove toxic heavy metals from aqueous solutions was increa-singly paid attention. In order to improve the soption ability of montmorillonite, various polyoxy cations(Zr⁴⁺, Al³⁺, Si⁴⁺, Ti⁴⁺) , surfasctants(quaternary ammonium cations) and acid activation were widely used to alter the surface properties . In fact, soption ability of montmorillonite depends on electrokinetic behavior of colloid suspension. The values of ζ-potential have a prominent effect on its adsorptive affinity for metal cations. Therefore, the main attempts in this work are focused on ζ-potential of montmorillonite , and the relationships between montmorillonite ζ-potential and adsorption capacity for Cr(Ⅲ). Various chelates were utilized to regulate montmorillonite ζ-potential in order to find a effective method which could improve the adsorption capacity of montmorillonite for Cr(Ⅲ). The results show that the adsorption capacity is ζ-potential-dependent, and increased greatly with its negative value increasing. The ζ-potentials of montmorillonite modified by chelates were changed evidently, and took place reversal from negative to positive after modified by 1,10-phenanthroline chelates. The effect of cation exchange adsorption depended on absolute values of ζ-potential, which before adsorption must be higher than that after adsorption. It was also found that modified montmorillonite showed higher adsorption capacity with more difference values of ∣ζ∣-potential between before and after adsorption. The adsorption quantity of Cr(Ⅲ) on montmorillonite could be double when ζ-potential was regulated by 1,10-phenanthroline chelates. Therefore, the cation exchange adsorption capacity of montmorillonite, which ζ-potential regulated by chelates, could be improved greatly.

Key words: Montmorillonite; ζ-Potential; Chelate; Cr(Ⅲ); Adsorption